Light-Emitting Device and Luminaire Incorporating Same

ABSTRACT

A light-emitting device includes a lens of refractive index n having a spherical exit surface of radius R and a luminous element positioned such that at least a portion of an edge of an emitting surface of the luminous element lies on a sphere of radius R/n opposite the exit surface, whereby that portion of the edge of the emitting surface is aplanatically imaged by the spherical exit surface. The light-emitting device may further include one or more reflective sidewalls arranged to reflect a fraction of light emitted from the luminous element before it is refracted by the exit surface. A luminaire incorporating a housing and a light-emitting device of this type is also provided, which may include one or more additional optical elements such as reflectors or lenses to further direct and shape light from the light-emitting device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 14/917,923, filed on Mar. 9, 2016, which is a U.S.National Stage of International Application No. PCT/US2013/059545, filedSep. 12, 2013, incorporated by reference herein.

BACKGROUND 1. Field of the Invention

The present invention relates to light sources for illumination, andmore particularly to light-emitting devices and luminaires havingrefracting and reflecting surfaces to alter the distribution of lightfrom a luminous element.

2. Description of the Related Art

Light-emitting elements (LEEs) are ubiquitous in the modern world, beingused in applications ranging from general illumination (e.g., lightbulbs) to lighting electronic information displays (e.g., backlights andfront-lights for LCDs) to medical devices and therapeutics. Solid statelighting (SSL) devices, which include light-emitting diodes (LEDs), areincreasingly being adopted in a variety of fields, promising low powerconsumption, high luminous efficacy and longevity, particularly incomparison to incandescent and other conventional light sources. Aluminaire is a lighting unit that provides means to hold, position,protect, and/or connect one or more light-emitting elements to anelectrical power source, and in some cases to distribute the lightemitted by the LEEs.

One example of a LEE increasingly being used for in luminaires is aso-called “white LED.” Conventional white LEDs typically include a“pump” LED that emits blue or ultraviolet light, and a phosphor or otherluminescent material. The device generates white light viadown-conversion by the phosphor of a fraction of the blue or UV lightfrom the LED (referred to as “pump light”) to light of a red, yellow, orgreen wavelength, or a combination of wavelengths longer than that ofthe pump light, and the mixing of light having these various wavelengthsfrom the pump and phosphor. Such white LED devices are also referred toas phosphor-converted LEDs (pcLEDs). Although subject to some losses dueto the light conversion, various aspects of pcLEDs promise reducedcomplexity, better cost efficiency and durability of pcLED-basedluminaires in comparison to other types of luminaires. In conventionalpcLEDs, a phosphor is often coated directly onto the semiconductor dieof the pump LED or suspended within an encapsulant very close to thesemiconductor die within the LED die package. In this position, thephosphor is subjected to the high operating temperature of thesemiconductor die, and it is difficult to design and fabricate a diepackage with excellent angular color uniformity.

Recently, light sources have been introduced in which a phosphor iscoated onto, or suspended within, a larger substrate that is separatedspatially somewhat from the LED die package instead of incorporating itclose to the die. Such a configuration may be referred to as a “remotephosphor.” Increasing the separation of the phosphor from the pump LEDprovides many potential benefits including better color control, highersystem efficiency and luminous efficacy, lower operatingtemperature—leading to higher reliability (lumen maintenance) and colorstability, design freedom to shape the emitting surface, and lower glarefrom a larger emitting surface. The remote phosphor approach is drivingrapid advancement in high-power and high-efficiency solid-state lightsources for general lighting. Together with the improvements in luminousefficacy that are associated with the LED light sources themselves,there is also a push for improved optics to direct the light where it isneeded with high efficiency, which is another component of energyefficiency.

Large-area remote phosphor elements, often packaged together. e.g. witharrays of pump LEDs placed in so-called “mixing chambers,” behave asLambertian emitting surfaces that are good for wide-angle ambientlighting when placed in simple luminaires having little or no secondaryoptics (i.e., optics outside of the LED package) for shaping the lightdistribution. But compared to the more point-like earlier-generationwhite LEDs, it is more difficult to design and manufacture efficientoptics to tailor the light distribution from these extended-sourceluminous elements, especially for applications needing narrower beampatterns or steep cutoff at the beam edges. Certain conventionalapproaches to making narrower or steeper patterns result in unwantedlosses in efficiency, as some light from the luminous elements isblocked rather than redirected into the desired beam pattern. Similarly,using conventional imaging optics to generate image-forming designs,even by experienced practitioners, generally results in systems of largesize and having significantly less than the maximum possible opticalefficiency. Currently, a relatively small proportion of designers arewell versed in the young specialty of nonimaging optics, which, as therelevant discipline for light-emitting devices and luminaires forillumination, rigorously analyzes and enables designs achieving themaximum thermodynamic limits for efficiency. In addition, much of thenonimaging optics theoretical literature is related to light-collectingconcentrators rather than to light-emitting devices. Design of opticsfor LEDs and luminaires thus lags somewhat behind the rapid advancementsin high-power LED light sources themselves.

There is accordingly an ongoing need for novel light-emitting devicesand luminaires designed to operate efficiently in conjunction withLambertian extended sources such as those using remote phosphor luminouselements, using simple to fabricate refractive and/or reflectivesurfaces, and with the ability to tailor the far-field patterns to haveuseful profiles for a variety of general lighting applications.

SUMMARY

Accordingly, the present technology provides light-emitting devices andluminaires having lenses of refractive index n with spherical refractiveexit surfaces and that are designed to operate efficiently inconjunction with extended source luminous elements having, in someembodiments, a disk shape. This is accomplished by positioning the edgeof the emitting surface of the luminous element on a notional sphere ofradius R/n opposite the exit surface (or radius Rn₀/n if the device isemitting into a medium of index n₀), so that at least a portion of theedge of the emitting surface is aplanatically imaged by the sphericalexit surface. Aplanatic “sharp” imaging results in a well-controlledangular distribution of those edge rays that are directly incident onthe exit surface and transmitted into the medium by the sphericalsurface with little or no primary aberrations. The primary monochromaticaberrations of spherical aberration and coma, as well as astigmatism,tend to broaden and blur the edges of the far-field angular distributionof the transmitted edge rays for a spherical lens operated away fromthis aplanatic condition, which may be detrimental to the far-field beampattern, especially for applications needing narrower beam patterns orsteep cutoff at the beam edges. Thus, unless appropriately controlled,aberrations could reduce the efficiency of the light-emitting devicewith regard to the proportion of emitted light that falls within adesired beam pattern.

In some embodiments, one or more reflective sidewalls are provided aspart of the lens, or as one or more separate pieces, to redirect lightrays that emerge from the luminous element at higher divergence anglesfrom the optical axis. These reflective sidewalls or other reflectorscan be used alone or in combination to further direct and shape thelight emerging from the light-emitting device, for example to makenarrow far-field beam patterns or steep cutoff at the beam edges.Reflective sidewalls can operate, e.g., by total internal reflection(TIR), or use reflective coatings directly on the lens, or comprise aseparate reflector adjacent the lens sidewall. Reflective sidewalls canbe configured so that there is a maximum of one reflection before a rayis incident on the exit surface, which can help provide good opticalefficiency. Reflective sidewalls can be conical, or shaped to ensureTIR, e.g., using an equiangular spiral shape for at least a portion ofthe sidewall, or can include two or more differently-shaped portions orfacets. In addition, one or more separate reflectors can redirect lightescaping the sidewall back into the lens to improve efficiency, or ifpositioned or extended beyond the exit surface, they can be used toredirect and/or shape some of the light leaving the refractive exitsurface at higher divergence angles, or both.

In some embodiments, a luminaire is provided that includes a housingsupporting a light-emitting device. A luminaire can further include anoptical element to further direct and shape or filter the light from thelight-emitting device, where the optical element can be a reflector,lens, filter, diffuser, or other optical element.

Embodiments of light-emitting devices may exhibit high efficiencywithout the use of special coatings on the spherical exit surface, bygeometrically arranging for all rays emitted by the luminous element tobe incident upon the exit surface at less than the critical angle forTIR. In those embodiments using a reflective sidewall, for example,internal reflection losses can be further reduced by arranging for allrays to be incident on the exit surface at angles that do not exceed aneven smaller angle than the critical angle, such as the Brewster angle.

More specifically, in certain embodiments, a light-emitting device hasan optical axis, which radiates light into a medium of refractive indexn₀. The light-emitting device has a lens of refractive index n with aconvex spherical exit surface of radius R centered on the optical axis,and a luminous element having an emitting surface that is opticallycoupled to, and emits light into, the lens. The luminous element ispositioned such that at least a portion of an edge of the emittingsurface lies approximately (e.g., within reasonable manufacturingtolerance) on a notional sphere of radius Rn₀/n having the same centerof curvature as the lens, with the emitting surface approximatelycentered on the optical axis opposite the exit surface across the centerof curvature, whereby that portion of the edge of the emitting surfaceis substantially aplanatically imaged by the spherical exit surface ofthe lens.

Certain embodiments feature a luminaire with a housing and alight-emitting device supported by the housing. The light-emittingdevice, which has an optical axis and emits into a medium of refractiveindex n₀, has a lens of refractive index n with a convex spherical exitsurface of radius R with the center of curvature disposed along theoptical axis, and a luminous element. The luminous element has anemitting surface optically coupled to, and emitting light into, thelens, and is positioned such that at least a portion of an edge of theemitting surface lies approximately on a notional sphere of radius Rn₀/nhaving the same center of curvature as the lens. The emitting surface isapproximately centered on the optical axis opposite the exit surfaceacross the center of curvature, whereby that portion of the edge of theemitting surface is substantially aplanatically imaged by the sphericalexit surface of the lens.

Other features and advantages will be apparent to those of ordinaryskill in the art upon reference to the following detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a light-emitting device having aspherical exit surface;

FIG. 2 is a cross-sectional view of a light-emitting device having atruncated back surface;

FIG. 3A is a cross-sectional view of a light-emitting device having aflat disk luminous element;

FIG. 3B is a cross-sectional view of a light-emitting device having adomed luminous element;

FIG. 4 is a cross-sectional view of a light-emitting device having aconical reflective sidewall;

FIG. 5 is a cross-sectional view of a light-emitting device having aconical sidewall with a reflective coated area;

FIG. 6 is a cross-sectional view of a light-emitting device having aconical sidewall and reflector;

FIG. 7 is a cross-sectional view of a light-emitting device having acurved reflective sidewall;

FIG. 8 is a cross-sectional view of a light-emitting device having acurved reflective sidewall whose opening terminates within a notionalBrewster sphere;

FIG. 9 is a cross-sectional view of a light-emitting device having aback curved reflective sidewall portion whose opening terminates withina notional Brewster sphere, and a front conical reflective sidewallportion;

FIG. 10 is a cross-sectional view of a light-emitting device having aback reflective sidewall including multiple differently-shaped portions,whose opening terminates within a notional Brewster sphere, and a frontconical reflective sidewall;

FIG. 11 is a normalized polar directivity plot of luminous intensity asa function of polar angle, showing the far-field beam pattern of thelight-emitting device shown in FIG. 10;

FIG. 12 is a rectangular plot of luminous intensity as a function ofpolar angle, also showing the far-field beam pattern of thelight-emitting device shown in FIG. 10; and

FIG. 13 is a cross-sectional view of a luminaire incorporating alight-emitting device like that of FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

While the configuration and performance of various embodiments arediscussed in detail below, it should be appreciated that the conceptsdescribed can be embodied in a wide variety of specific contexts. Thespecific embodiments discussed herein are thus merely illustrative ofspecific ways to make and use the invention and are not intended todelimit the scope of the invention.

Nonimaging optical design depends primarily on the edge ray principle(W. Welford and R. Winston, The Optics of Nonimaging Concentrators, NewYork: Academic Press, 1978) to design optical systems having highoptical efficiency. According to the edge ray principle, an ideal system(having maximum theoretical concentration and efficiency) transmittingradiation from an entry aperture to an exit aperture has the propertythat extreme rays of the entry aperture pass the exit aperture likewiseas extreme rays. All other rays originating within the entry aperturetraverse the system to lie at angles and/or positions within those ofthe extreme rays, and are thus also transmitted without loss. The edgeray principle was originally developed to describe reflecting opticalsystems, but has since been generalized to include refractive systems.Similarly, although nonimaging optics was originally formulated forapplication to concentrating systems, in which light incident on anoptical system over a range of angles is concentrated to a smaller area(over a larger range of angles), it has since been applied toillumination systems in which light from a light source emitting over arange of angles is “collimated” by an optical system to emerge from alarger aperture over a smaller range of angles. The edge-ray designprinciple as applied to light sources can be formulated as follows: raysoriginating at an edge point of the extended light source shouldpropagate at the maximum divergence angle of the output beam afterleaving the collimator. Rays originating at points within the edge ofthe light source should all emerge at angles within the maximumdivergence angle. Satisfying this condition leads to well-formedfar-field patterns with desirable edge steepness (light remaining withina designed maximum divergence angle).

Referring now to FIG. 1, a cross-sectional view of an embodiment of alight-emitting device 100 is shown for the purpose of discussing theprinciples of operation and fundamental geometry. Light-emitting device100 is designed to emit light generally in the positive-z direction; theterms “front” versus “back” (or “rear”), or “forward” versus “backward,”will be used to refer to the directions, or parts located toward,positive-z versus negative-z, respectively. A spherical lens 110 ofradius R, including an optical material that is transparent towavelengths of interest, has a center of curvature 150 at theintersection of an optical axis 140 that is parallel to the z axis asshown by the coordinate system at the upper right of the figure and anequatorial plane 145 that is parallel to the x-y plane. The equatorialplane 145 is the plane that is normal to the optical axis 140 and thatincludes the center of curvature 150. (In the interest of clarity and toreduce clutter, FIG. 1 and other similar views shown herein omitcross-hatching that would normally indicate the transparent material ofthe lens in cross-sectional drawings.) Lens 110 is immersed in a mediumof unity refractive index, into which light-emitting device 100 emitsthrough spherical exit surface 115 of lens 110. [Note that with no lossof generality, all dimensions and expressions described herein can bescaled correctly, with the light-emitting device immersed in a medium ofrefractive index n₀ instead of unity, simply by replacing the value n inthose dimensions and expressions with the ratio (n/n₀).] A light source,luminous element 120, that emits light in the positive z direction isembedded in the material of lens 110. Such a light source can have, forexample, an electroluminescent surface, or have an emitting surfaceincluding a phosphor that is optically pumped from a separate pump lightsource. Only the emitting surface of the luminous element is shown forsimplicity; as discussed later, there may be other components of theluminous element that are necessary for its operation but that need notbe optically interfaced directly to lens 110 and thus are not necessaryto show in order to explain the principle of operation of light-emittingdevice 100. Luminous element 120 has maximum radial extent r as measuredalong a normal to the optical axis 140. The emitting surface of luminouselement 120 in this embodiment is shaped as a portion of a sphere, andarranged to lie on a notional sphere 125 of radius R/n (or Rn₀/n if lens110 is immersed in a medium of index n₀), centered on the same center ofcurvature 150 within lens 110, and centered on optical axis 140 on thenegative-z side of notional sphere 125 opposite vertex 146 of lens 110,which vertex is located on optical axis 140 at the greatest positive-zextent of lens 110. Henceforth, notional sphere 125 shall sometimes bereferred to as “the R/n sphere.” For purposes of this discussion, FIG. 1and similar drawings depict light-emitting devices with axial(infinite-fold rotational) symmetry about optical axis 140, such thatthe emitting surface of luminous element 120 is envisioned to have acircular edge 126, but the emitting surface can be shaped in ways otherthan circular, such as square or rectangular, so long as the maximumradial extent to the corners is equal to r, and the corners lie close tothe notional R/n sphere 125.

With this placement of the emitting surface of luminous element 120lying on R/n sphere 125, all points of the emitting surface areaplanatically imaged by exit surface 115 of spherical lens 110 to form asharp virtual image 130 of the luminous element, positioned to lie on anotional sphere 135 having radius nR (or nR/n₀) and having radial extentn²r as shown. In other words, virtual image 130 is formed with a lateralmagnification of n² in the medium of unity index, or more precisely,(n/n₀)², if the medium outside lens 110 has refractive index n₀.Notional sphere 135 shall also be referred to as “the nR sphere.” Thatimage 130 is a virtual image means that light rays emitted by points onluminous element 120 appear to be emanating from corresponding points onvirtual image 130, when viewed from the medium outside lens 110 andlooking back into lens 110 in the negative-z direction. Aplanaticimaging means that points on virtual image 130 are imaged sharply withno spherical aberration or coma; for this configuration of sphericalexit surface 115 and light source 120, the Abbe sine condition issatisfied, and all points of virtual image 130 are also imaged free ofastigmatism, which is another primary aberration. In an application ofthe edge ray principle, points on the edge 126 of the emitting surfaceof luminous element 120 should be imaged to edge 136 of the virtualimage substantially free of aberrations. Deviations of points on theluminous element 120 away from lying exactly on the R/n sphere 125result in an increase in aberrations, a less-sharp virtual image, andthus some blurring of the edges of the beam pattern. The optical effectsof such deviations can be quantified and comprehended in a design and/orin the presence of fabrication errors to achieve a certain acceptablelevel of performance. For this reason, edge 126 of luminous element 120may be arranged to lie “approximately” rather than exactly on R/n sphere125, since the emitting surface will be substantially aplanaticallyimaged with a known and limited degradation in performance from perfectconstruction. Small deviations in any direction from R/n sphere 125 canbe tolerated within predetermined tolerances. Likewise, since lightsources for illumination emit over a range of wavelengths, and practicalmaterials for lens 110 exhibit optical dispersion such that therefractive index n is a function of wavelength, even aperfectly-fabricated device should have exactly ideal performance atonly one wavelength. It should also be noted that because of sphericalsymmetry of the entire system, any shift of the center of luminouselement 120 away from the drawn optical axis 140 (while edge 126 remainson notional sphere 125) is expected to simply redefine a new opticalaxis about which the far-field pattern is centered, and thus aside frompointing in a different direction, the far-field pattern performance interms of beam divergence will be undiminished.

The far-field beam pattern of the light-emitting device of FIG. 1, for aluminous element 120 having relatively small lateral extent r, so thatedge 126 lies close to optical axis 140, is Lambertian (falls off as acosine function) out to a cutoff divergence half-angle equal to thecritical angle of total internal reflection (TIR) given by arcsin(n₀/n).This cutoff occurs due to high internal reflection of rays emitted closeto horizontal (nearly parallel to the x-y plane) from luminous element120. This situation can be understood more fully with reference to FIG.2, which shows sectional view of a light-emitting device 200 accordingto another embodiment, having lens 210 with exit surface 215, andluminous element 220 with edge 226, configured similarly to those inFIG. 1. Again, luminous element 220 is assumed to emit in a Lambertianpattern towards the half-space of positive z within lens 210, and it isplaced on notional R/n sphere 125 so that all points of virtual image230 are formed aplanatically. Light emitted horizontally from on-axispoint 225, known as the Weierstrass point, would strike exit surface 215exactly at the critical angle for TIR, and be imaged to correspondingon-axis point 235 in the virtual image 230. With this shallow sphericalshaped emitter, edge 226 of luminous element 220 shadows horizontal raysfrom Weierstrass point 225, but horizontal rays from edge 226 strikeexit surface 215 at nearly the critical angle. Extreme ray 250 emergeswith an angle to optical axis 140 that is close to the critical anglefor TIR, and appears to be emanating from near image point 235. Thereare no rays from luminous element 220 incident on exit surface 215 withnegative z components. Thus lens 210 will operate in the same way aslens 110 in FIG. 1 even if segment 245 of the sphere below the luminouselement is entirely removed or truncated. In FIG. 2 and similardrawings, portions of the lens that can be, or have been, removed ortruncated are indicated by a bold phantom line, and the remainingexposed surface 240 of lens 210 will be referred to as a truncatedsurface 240. Annular truncated surface 240 has no primary opticalfunction since there are essentially no direct rays from luminouselement 220 incident upon it, except perhaps for stray rays that mayoccur due to manufacturing errors and that may be emitted from edge 226above surface 240 with small negative-z components. Thus surface 240need not be smooth or otherwise of optical quality, unless as asecondary consideration, for example, it is desired to implement areflector here to redirect internal Fresnel reflections from exitsurface 215 to recycle them for added efficiency.

Besides removing unnecessary lens material, saving cost and weight,truncating lens 210 as shown in FIG. 2 has the additional advantage ofallowing access to the back side of luminous element 220, so that itsemitting surface can be assembled or deposited onto lens 210 withoutrequiring complete immersion in the lens material, and additionalstructures associated with luminous element 220, or required to operateluminous element 220, such as electrical connections, pump LEDs, canalso be placed outside lens 210.

FIGS. 3A and 3B depict exemplary light-emitting devices in which, whilethe edge of the emitting surface of the luminous element liesapproximately on the R/n sphere 125 in accordance with the edge rayprinciple, points within the edge of the emitting surface and closer tothe optical axis 140 deviate from lying on the R/n sphere 125. Thedeviation is intentional in these examples, rather than due tofabrication error, and is due to the three-dimensional shape of theemitting surface, which unlike in FIGS. 1 and 2, does not follow theshape of the R/n sphere 125. While the edge of the emitting surface ofthe luminous element is placed near the R/n sphere 125, points on theemitting surface closer to the optical axis can deviate on either sideof the R/n sphere and still satisfy the edge ray principle, as will beexplained shortly. Thus the luminous element can be more concave (havinga smaller radius of curvature) than the R/n sphere, or flatter, orconvex toward the front (domed), or irregular and deviating on eitherside of the surface of the R/n sphere. FIG. 3A shows a light-emittingdevice 300 a in which luminous element 320 a is a flat disk such thatits emitting surface is approximately planar, and FIG. 3B shows alight-emitting device 300 b in which luminous element 320 b is domed,having an emitting surface that is convex toward the front (i.e., towardpositive z).

Specifically, FIG. 3A illustrates a sectional view of a light-emittingdevice 300 a with lens 310 a having exit surface 315 a, in whichtruncation of lens 310 a to produce a flat truncated surface 340 afacilitates placement or attachment of a luminous element 320 a having aflat disk shape of radial extent r. Again, annular truncated surface 340a is not necessarily of optical quality, since it has no primary opticalfunction. But in this case, the area of lens 310 a (closer to opticalaxis 140 than annular truncated surface 340 a, with inner edge at radiusr) to which luminous element 320 a is optically coupled should be ofoptical quality, or it should be effectively index matched to theemitting surface of luminous element 320 a with gel or adhesive suchthat roughness does not cause unwanted scattering of light emitted fromluminous element 320 a. Edge 326 a of luminous element 320 a is arrangedto lie on notional sphere 125 as before. Thus the edge ray principle isapplied as before, and edge 326 a is aplanatically imaged by exitsurface 315 a. Points lying on the emitting surface of luminous element320 a at smaller radii than r from the optical axis 140 are notaplanatically imaged, since they do not lie exactly on the R/n sphere125. But the virtual images of those points at smaller radii (notshown), although fuzzy and enlarged by aberrations, are entirelycontained within the sharp circular-edged image of edge 326 a. Thus norays from inside R/n sphere 125 violate the edge ray principle, and thebeam pattern does not suffer. The smaller the radial extent r of a flatdisk source, the closer it approaches a point source on-axis at theWeierstrass point, and the closer all points on the disk lie to the R/nsphere 125. Smaller disks also cast narrower and sharper far-field beampatterns. As a flat disk source 320 a increases in diameter, while itsedge remains on the R/n sphere 125, it approaches the equatorial plane145, and the far-field pattern changes shape and broadens, lookingincreasingly Lambertian except for some flattening due to internalreflection losses that redistribute the flux. Therefore, the most usefulpatterns from hyperhemispherical light-emitting devices such as thoseshown in FIGS. 1-3A and 3B are obtained with sources having relativelysmall radii r, for example for luminous elements whose edges lie lessthan half-way along the R/n sphere, so that, e.g., r<(1/√2)(Rn₀/n). Allof the depicted embodiments meet this criterion. Note also that thevirtual image (not shown) of a flat disk source 320 a lies on aspherical Petzval surface that is convex toward positive z. Petzvalcurvature is the primary source of field curvature, so that a virtualimage of a non-circular luminous element would experience somedistortion in addition to the aberrations already discussed.

FIG. 3A also shows an exemplary configuration of a luminous element of aremote phosphor type in schematic fashion. Flat disk remote phosphor 320a is excited by a pump arrangement represented schematically by a pumpsource 370 including a pump LED 380, shown with a semiconductor die(typically emitting at a blue wavelength) and its own dome-shapedencapsulating lens, and a mixing chamber 385 typically includingdiffusely-reflecting surfaces that collect, redirect, and uniformizerays from the pump LED such that the remote phosphor disk of luminouselement 320 a is illuminated uniformly across its surface. The remotephosphor disk absorbs blue pump light and re-emits at yellow, green,and/or red wavelengths, while elastically scattering some of the bluepump light. The light that emerges from the pump disk in the generallyforward direction into the lens 310 a typically is thus a mixture ofwavelengths including scattered pump light and re-emitted light from thephosphor, designed to appear white with a particular color temperatureto the human eye. While this represents a typical current implementationof a luminous element such as 320 a, others are certainly possible,including any light source that can be integrated into a light-emittingdevice according the present invention. (FIG. 3B also shows this type ofpump arrangement, used with a domed phosphor.) In most of the remainingfigures, for simplicity, representations of flat disk sources of thistype generally omit and will not depict the details of the pump source370, since the lens and reflector optics do not depend on these details,but rather only the position of the emitting surface of the luminouselements (such as 320 a).

Besides a flat disk, a domed phosphor that is convex toward the exitsurface is also possible. Such an arrangement is illustrated in FIG. 3B,which shows a light-emitting device 300 b with a hyperhemispherical lens310 b, in this case with a convex domed luminous element 320 b opticallycoupled to lens 310 b and positioned such that edge 326 b of theemitting surface of luminous element 320 b lies approximately on R/nsphere 125. Again, luminous element 320 b is approximately centered onoptical axis 140 on the opposite (negative-z) side of R/n sphere 125from the positive-z vertex of exit surface 315 b. Lens 310 b has aconcave depression to accept luminous element 320 b, which may beintegrally formed into or onto lens 310 b, or attached usingindex-matching material. Luminous element 320 b can be domed more orless than is shown, and although drawn that way, need not be shaped as aportion of a sphere. Luminous element 320 b is shown schematically, andthe thickness of the line in the drawing representing it is notphysically significant; a significant feature is the shape of theemitting surface. For example, the overall thickness of luminous element320 b need not be uniform, but a phosphor layer may be e.g. coated ontoa lens-shaped substrate that is either thicker or thinner in the centerthan the edge, and that is transparent to the pump wavelength emitted bylight-emitting diode 380. Or, in an alternative configuration ofluminous element 320 b, a convex lens-shaped transparent body can befilled with a suspension of phosphor particles distributed within it. Inthe case of a domed luminous element 320 b, more care may need to betaken with truncated surface 340 b, since some rays from luminouselement 320 b will be have a component in the backward direction(negative z component), and thus will be incident on surface 340 b. Forexample, truncated surface 340 b can be made reflective, in order todirect light back toward the positive z direction for refraction by exitsurface 315 b, and thereby increase the optical efficiency. Similarly, alight-emitting device 300 b having a domed luminous element 320 b maybenefit from additional reflective sidewall features to be discussednext in conjunction with FIG. 4 and following figures.

Exemplary embodiments shown heretofore have depicted lenses of sphericalor hyperhemispherical shape. Such shapes can present some challenges infabrication. Furthermore, although the far-field patterns of theselight-emitting devices are well-behaved, there are inefficienciesarising from the internal reflection losses experienced by a fraction ofthe rays incident on the exit surface at angles approaching the x-yplane, i.e., more horizontal, and, to achieve narrower beam patterns,more rays could be directed toward the optical axis. A separatereflector optically coupled to receive light from the exit surface andredirect it forward can be added to the light-emitting device, in oneembodiment. But it is desirable to incorporate features into lens of thelight-emitting device to control the light distribution so that feweroptical surfaces are encountered and higher efficiency is achieved.Embodiments will now be shown in which the exit surface is hemisphericalor a smaller portion of a sphere, and in which additional features areincorporated so that the light-emitting device can radiate more lightinto a narrower range of forward angles, while ensuring that internalreflection losses are held low. While it would be possible toincorporate an optical aperture into a lens to limit the range of anglesthat rays pass through the lens, this approach is likely to increaselosses because apertures operate by blocking rays rather thanredirecting them. Thus, instead of apertures, reflecting features,either built into the lens or separate, will be provided that redirectsome rays propagating at larger angles to the optical axis to exit thelens at smaller angles to the optical axis. Properly designed, thesereflecting features can also be used to reduce internal reflectionlosses by ensuring that all rays are incident on the exit surface atangles less than a predetermined maximum incidence angle. One possiblechoice of a reflecting feature is, for example, a conical sidewallextending backward from the exit surface, e.g., starting at a radiusfrom the optical axis that is a large fraction of R, at least part waytoward the emitting surface of the luminous element, with a size andcone angle selected to intercept a given fraction of high-angle rays andredirect them in a more forward direction. But more control overinternal reflection loss is provided by the embodiments to be describednext.

FIG. 4 shows a cross-sectional view of a light-emitting device 400having a lens 410 with a hemispherical exit surface 415 truncated withannular surface 440 at equatorial plane 145. Again, truncated surface440 has no primary optical function, and it can be used, e.g., formechanical alignment or mounting. A reflective sidewall 430 of conicalshape has been added, extending from a back edge 432 close to the edge426 of luminous element 420 to a front edge 438 in the equatorial plane.This choice of location for front edge 438 is somewhat arbitrary, andhas been selected to coincide with the inner edge of flat truncatedsurface 440. This choice for the position of front edge 438 results inan aperture as large as possible with a hemispherical exit surface 415.Positioning front edge 438 on the R/n sphere 125 also ensures that anyrays transmitted through the aperture or reflected from sidewall 430 areincident on exit surface 415 at angles that do not exceed the criticalangle for TIR. This is another property of the R/n sphere 415, that anyray originating within it, or appearing to originate from within it, isnecessarily incident on the exit surface 415 at radius R at an angleless than the critical angle. Example rays 450 and 460 show,respectively, a ray 450 that is incident at the greatest possible anglefrom the optical axis 140 from edge 426 and barely skimming the edge 438of the conical reflector on the opposite side of optical axis 140, andray 460 that is reflected off of the opposite conical reflectivesidewall 430. It can be seen that there is still a segment of thehemispherical exit surface 415, below ray 450 and toward the equatorialplane 145 that has no rays incident on it.

FIG. 5 shows a light-emitting device 500 similar to that of 400 in FIG.4, but with some additional features. Depending on the details ofrefractive index and dimensions of the luminous element 520, a conicalsidewall 530 may not be inherently reflective by TIR all the way down tothe back edge. That is, rays such as 560 that strike sidewall 530 backtoward the luminous element 520 may not be guaranteed to experiencetotal internal reflection, because they may be incident on sidewall 530at angles less than the critical angle. This is particularly likely forrays originating at the opposite edge 526 of luminous element 520. Thusan additional reflective area 535 such as a reflective coating onsidewall 530 or a separate reflector outside the sidewall may benecessary to guarantee reflection of these rays, at least along the backportion of the sidewall as shown in FIG. 5. Coatings 535 or additionalreflectors may not be required toward front edge 538 of the sidewall530. Lens 510 is assumed here, as in the other illustrated embodimentsto be a single piece of transparent material with exit surface 515 aswell as conical reflective sidewall 530 integrally formed into it. Lens510 could be made in more than one piece and held together with indexmatching material between the parts to minimize reflections at theinterfaces.

As mentioned before, back corner 532 need not be exactly coincident withedge 526 of luminous element 520, and it need not lie on R/n sphere 125;it just needs to be positioned such that reflective sidewall 530 canintercept all desired rays. In FIG. 5, this situation is illustratedwith the back edge 532 extending below the R/n sphere 125. Luminouselement 520 is positioned with its edge 526 on R/n sphere 125, and assuch its emitting surface can be disposed within a recess in the backend of the lens 510. This is just one example of how the requirements ofthe optical configuration of the present invention can be satisfied inmultiple ways while allowing variations that can, e.g., simplifyfabrication or mechanical mounting.

FIG. 5 also demonstrates the truncation of lens 510 to eliminateoptically unnecessary segment 545, leaving truncated surface 540, as waspreviously discussed in connection with FIG. 4. Ray 550 demonstratesthat the most extreme rays do not strike truncated surface 540.

To further limit internal Fresnel reflection losses, instead of limitingincidence angles on the exit surface to less than the critical angle forTIR, a smaller angle can be prescribed. A convenient choice is theBrewster angle given by arctan(n₀/n). This is the angle for whichinternal reflection losses are zero for one polarization, and are smallfor the other polarization. The total reflection losses are relativelyflat from zero incidence to the Brewster angle, after which theyincrease rapidly to 100% at the critical angle. Thus the Brewster angleis a good choice for a limiting internal incidence angle. Like the R/nsphere, there exists a Brewster sphere of smaller radius Rn₀/√(n₀ ²+n²),such that any ray originating within it, or appearing to originate fromwithin it, is necessarily incident on the exit surface at an angle lessthan the Brewster angle.

FIG. 6 shows a light-emitting device 600 in which a lens 610 has aconical sidewall 630 extending from the outer edge of the luminouselement 620 to the exit surface 615. The conical sidewall is chosen tobe at an angle such that it intersects Brewster sphere 155 in theequatorial plane 145. This sidewall may not exhibit TIR for all rays,and hence a supplementary separate reflector 635 is shown (slightlyseparated from the sidewall 630 for schematic purposes to indicate thatit is not a coating) that can be used to reflect rays back into the lensthat would otherwise escape the sidewall. Separate reflector 635 canalso be constructed, as shown in FIG. 6, to extend past the exit surface615 forward into the medium; some rays that are transmitted into themedium by exit surface 615 at large angles from the optical axis 140 canstrike this reflector 635 and thereby be further directed toward theoptical axis 140. In general, reflector 635 need not extend the entirelength of the lens, or forward past the lens, and as one possibility, itcan extend from adjacent exit surface 615 some distance toward positivez, to further direct and/or shape the light emitted from exit surface615, even if TIR occurs farther back within the lens in light-emittingdevice 600, and reflector 635 is not needed toward the back. Reflector635 can have the same shape as sidewall 630 and run parallel to sidewall630 where they overlap along the length as shown in FIG. 6, or theshapes of reflector 635 and sidewall 630 can be different from eachother. The reflector 635 is shown as a single straight cone, but can beshaped differently outside the lens 610, or reflector 635 and sidewall630 can have matching, but varying shapes as they progress along thelength of light-emitting device 600 in order to tailor the beam patternor to guarantee various reflection angles. For example, sidewall 630and/or reflector 635 can have different shapes along the portionslabeled 655, 665, 675, and 685 in FIG. 6. Portion 685 is that partclosest to luminous element 620 and extending within the R/n sphere 125.Portion 675 lies entirely within the Brewster sphere 155, so that ray670 is guaranteed to be incident on exit surface 615 at less than theBrewster angle. Portion 665 again lies within the R/n sphere 125, andthus guarantees incidence of rays like 660 at smaller than the criticalangle; but if properly shaped, or if dimensions and angles are checkedto make it so, it could also guarantee incidence of ray 660 and similarrays on exit surface 615 at less than the Brewster angle. But this needsto be intentionally designed. Finally, portion 655 lies outside R/nsphere 125, and so care has to be taken to ensure that all rays like 650hit exit surface 615 at less than the critical angle. It is possible,however, that even all these can be maintained below the Brewster angle.

For high efficiency and lowest losses, it is desirable to use TIRreflecting sidewalls when possible. It is known that when sidewalls areproperly shaped in the form of an equiangular spiral (also called alogarithmic spiral) having a design angle of incidence that is greaterthan or equal to the critical angle, this criterion can be met for allrays incident on the sidewall. Such a design is illustrated in FIG. 7,which shows a light-emitting device 700 having a lens 710 with exitsurface 715 and luminous element 720, where the reflecting sidewall 730is in the shape of an equiangular spiral originating adjacent theluminous element and extending to the equatorial plane 145, terminatingwithin the R/n sphere 125. Thus this configuration both guarantees TIRon the reflecting sidewall, and ensures the absence of TIR on exitsurface 715. Surface 740 has been truncated in a manner that it does notinterfere with extreme ray 750. In general, an equiangular spiral isdesigned to start at the outer edge of the emitting surface of luminouselement 720 at radius r. The parametric equation of an equiangularspiral starting from an edge of the luminous element is s(t)=2r exp(tang), where s is the distance to the curve from the point of origin or“unwinding,” which is the edge on the opposite side of the emittingsurface of luminous element 720, t is a parametric angle of unwinding,and g is the design angle of incidence, which is a constant for all raysoriginating from the point of unwinding and striking the spiral at eachpoint determined by t. But depending on the details of the size ofluminous element 720, the refractive index of lens 710 and/or at leastthe back portion of lens 710 containing the TIR portion, if it is madein more than one piece, it may be difficult or impossible to design anequiangular spiral that starts and stops at edges exactly at theselocations. In those cases, several options are available, since thelocations of the back and front edges are somewhat flexible as has beenseen earlier.

If the refractive index is high enough, then design angle g can be madesmaller and the spiral can be tightened up. This case is shown in thelight-emitting device 800 depicted in FIG. 8, the TIR sidewall 830equiangular spiral can be made narrower, e.g., beginning at the edge ofluminous element 820 and terminating as shown at the equatorial plane145 within Brewster sphere 155, guaranteeing angles of incidence of allrays such as ray 850 and ray 860 on the exit surface 815 of lens 810 ofless than the Brewster angle. Again, lens 810 is truncated at surface840 in such a manner as not to reflect rays like ray 850. However, inthe interest of further narrowing the beam pattern, further truncationof the front part of the lens, e.g., with a conical sidewall 840 havinga steeper angle, can be accomplished to reflect some of the large-anglerays like ray 850. This is the situation shown in FIG. 9.

FIG. 9 shows a light-emitting device 900 with all the features oflight-emitting device 800 in FIG. 8, but with the front portion of lens910 further truncated by removal of segment 945, leaving truncatedconical surface 940. In this case, surface 940 has an optical functionas a reflecting surface and should be smooth and polished, and possiblyreflectively coated if all rays like ray 950 do not experience TIR. Ingeneral, it is not difficult to ensure TIR on surface 940 due to itssteep angle. Reflective sidewall 930 is again shown as an equiangularspiral starting at luminous element 920 and terminating within Brewstersphere 155. Although it is not difficult to ensure TIR on truncatedsurface 940, care should be taken not to truncate to too narrow anangle, because beyond a certain point in narrowing the truncated surface940, TIR on exit surface 915 from rays like 950 that reflect fromsidewall 940 can occur. Light-emitting device 900 is depicted showing aluminous element 920 of remote phosphor type including its pumpstructure 370.

FIG. 10 shows a light-emitting device 1000 in which several of theforegoing concepts are all integrated. Luminous element 1020 is coupledto lens 1010 with spherical exit surface 1015 having a back reflectivesidewall 1030. Sidewall 1030 includes two portions of different shape,back portion 1034 in the shape of an equiangular spiral, and frontportion 1036 designed to be a straight-walled cone extending fromequatorial plane 145 back to the point of tangency of the equiangularspiral. The two portions accidentally happen to join close to wheresidewall 1030 crosses the Brewster sphere 155, although this is not bydesign. The use of two portions 1034 and 1036 of sidewall 1030 enablesfurther shaping of the far-field beam pattern. Incorporating more thantwo portions of sidewall in the direction along the optical axis (thelongitudinal direction) could provide even more control of the beampattern. Furthermore, reflective sidewall 1030 could be divided intoflat or curved facets in the azimuthal direction instead of, or inaddition to, the longitudinal direction, in order to achieve variouseffects in the beam pattern, such as homogenization of the beam patternof a nonuniform luminous element, or special effects. In addition, frontsegment 1045 of lens 1010 has been removed, leaving truncated surface1040, which acts as a TIR surface to further tighten the far-fieldpattern. In this actual design example, the angle of the ray 1050 beforereflecting off surface 1040 is just over 53 degrees. The truncatedsurface 1040 is set to an angle of 40.65 degrees from the optical axisto cause total internal reflection of some of the largest-angle rayslike ray 1050. The resulting beam patterns are shown in FIG. 11, whichshows a polar directivity plot of luminous intensity as a function ofpolar angle, which shows a very flat angular distribution across thecenter of the beam and a half-width half-maximum (HWHM) beam width ofjust under 30 degrees. Another plot of the same data but on rectangularaxes is shown in FIG. 12, in which the “skirts” can be seen to be verysteep, as is often desired in practical applications.

Additional embodiments include luminaires that include a housing tosupport one or more light-emitting devices. Such a luminaire may providemeans for mounting and aiming the one or more light-emitting devices,and may also optionally include means for connecting electrical power tothe one or more light-emitting devices. Additional optional opticalelements to further direct or shape the light pattern emanating from theone or more light-emitting devices can also be incorporated into aluminaire.

FIG. 13 shows a sectional view of an embodiment of a luminaire 1300 thatalso includes optional secondary optical elements. The luminaire 1300shown in FIG. 13 includes a light-emitting device 1360 (e.g., in thiscase resembling light-emitting device 900 shown in FIG. 9) and a housing1310 to support and protect the light-emitting device 1360. The housing1310 can include structures (not shown) to facilitate mounting of theluminaire 1300. The luminaire 1300 can provide means for electricalconnection of the light-emitting device 1360 to a power source outsidethe luminaire, for example. Electrical connection 1320 is shownschematically as a wire, but can include other connection means such asflex circuits, printed circuits, connector contacts, or other electricalconnection means known in the art. In some implementations, thelight-emitting device 1360 can be coupled to a cooling device 1330 suchas a heat sink. The optional cooling device 1330 can be used to removeheat from the area of the light-emitting element within thelight-emitting device 1360. The cooling device 1330 can be passive(including, e.g., fins for free convection), or can incorporate activecooling mechanisms such as fans or thermoelectric devices. The luminaire1300 can also include an optional electronic module 1340. The electronicmodule 1340 can include additional electronics such as conversionelectronics to convert mains power voltages and currents, which can be,for example, line-voltage AC, into voltages and currents of types (e.g.,DC) and levels suitable for driving the light-emitting element withinlight-emitting device 1360. Other functions can also be incorporatedinto the electronics module 1340, including, but not limited to,controllers for dimming, communication with controllers outside theluminaire 1300, and sensing of ambient characteristics such as lightlevels, the presence of humans.

Still referring to FIG. 13, the housing 1310 of luminaire 1300 can alsooptionally support an additional optical element, such as a reflector1350. The reflector 1350 can be used for direction, distribution, orshaping of the light that is output from light-emitting device 1360. Forexample, light emitted at large angles with respect to the axis of theluminaire 1300 and light-emitting device 1360 can be redirected into anarrower beam pattern in the far field of the luminaire 1300 by properdesign of the reflector 1350.

The luminaire 1300 shown in FIG. 13 further includes an optional lens1355 as an additional optical element coupled to the housing 1310. Thelens 1355 can be configured to perform additional optical functions thatalter a property of the light such as its directionality or spectrum.For example, lens 1355 can perform such functions as diffusing light toachieve a desirable pattern or reduce glare, and can incorporateadditional materials or structures to accomplish these functions, suchas suspended particles or surface or embedded microstructures. Lens 1355can also include materials or structures with spectrum-alteringproperties to perform functions such as wavelength filtering, e.g. usingabsorption or diffraction. As shown in FIG. 13, some embodiments ofluminaires can include both reflectors 1350 and lenses 1355.

The luminaire shown in FIG. 13 is an exemplary embodiment. Otherembodiments can use different configurations of reflectors or lenses,and different relative positions within the luminaire of thelight-emitting device with respect to the reflectors or lenses, as willbe apparent to those skilled in the art. For example, a reflector of adifferent shape and oriented differently from that shown in FIG. 13 canbe used to redirect light along an axis different from an axis of thelight-emitting device. In some implementations, a lens can be, forexample, a Fresnel lens, or a system of multiple lenses. Other functionsinstead of, or in addition to, directing or concentrating the light canbe performed by transmissive optical elements such as lenses, or byreflective optical elements such as reflectors. For example, eitherlenses or reflectors can have structures incorporated within them or ontheir surfaces, such as small-scale roughness or microlenses, designedto diffuse or shape the light in the far field. In some embodiments,combinations of reflectors and lenses, or systems of additionalreflective and/or transmissive optical elements can be used. Eithertransmissive or reflective optical elements can includespectrum-altering properties.

Additional alternative embodiments not pictured are also contemplated.For example, instead of a smooth spherical surface for the lens, thelens can have a stepped Fresnel surface. Lens materials can include anytransparent material, such as a transparent glass or a transparentorganic polymer (e.g., silicone, polycarbonate or an acrylate polymer,cyclic olefin polymers or cyclic olefin copolymers).

The luminous element can be self-luminescent, such as anelectroluminescent device, or a phosphor layer pumped optically asdescribed herein, that can be coated directly onto the lens, or coatedonto a separate flat or curved/domed substrate, or glued on using indexmatching adhesive, or attached otherwise with index matching gel orliquid, or a phosphor suspended in a bulk polymer and multi-shot moldedusing a thermoplastic or thermosetting process. The luminous element canbe a single element, or it can comprise multiple elements such as anarray of light sources arranged according to the extents prescribedherein, e.g., with those points of the array having the greatest radialextent r arranged to lie approximately on the R/n sphere.

Certain embodiments have been described. Other embodiments are in thefollowing claims.

1-28. (canceled)
 29. A luminaire, comprising: a housing; and alight-emitting device supported by the housing, having an optical axisand emitting into a medium of refractive index n₀, comprising: a lenshaving refractive index n and a convex spherical exit surface of radiusR with a center of curvature disposed along the optical axis, and aluminous element having an emitting surface optically coupled to thelens, the luminous element positioned such that at least a portion of anedge of the emitting surface lies approximately on a notional sphere ofradius Rn₀/n having the same center of curvature as the lens, and alsopositioned such that the emitting surface is approximately centered onthe optical axis opposite the exit surface across the center ofcurvature.
 30. The luminaire of claim 29, wherein the spherical exitsurface substantially aplanatically images the portion of the edge ofthe emitting surface.
 31. The luminaire of claim 29, further comprisingan optical element supported by the housing and configured to receivelight emitted from the light-emitting device and to alter a property ofthe received light.
 32. The luminaire of claim 31, wherein the opticalelement is configured to alter a directionality of the received light.33. The luminaire of claim 31, wherein the optical element is configuredto alter a spectrum of the received light.
 34. The luminaire of claim31, wherein the optical element is a reflector.
 35. The luminaire ofclaim 31, wherein the optical element is a lens.